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that's the tell tale bit. You never need to go in the dark to see the uranium glow, although you might need to get out of the sun, and you can generally wave your torch around from at least a foot away and get a reaction (depends a little on the lighting conditions). I don't always get it right.

Manganese was often used to decolorise glass. Silica sand often contains iron, which turns glass coke-bottle green; adding manganese turned it clear. Try your torch on some old clear drinking glasses. Quite why it pops up in amber and green glass (don't know if it's found in blue or pink, don't often pick that up), I don't know. It's probably something to do with adding your colorants to your standard clear mix or maybe they got better shades if they got rid of the iron green. Glass recipes were often very traditional.

Manganese fell out of favour when cheaper alternatives became available. Like uranium, it's never been cheap.

Used on its own in high concentrations, it gives a lovely purple. It is also what causes clear old glass to sun purple, or more likely sun grey here in the UK. The sun changes the chemical composition of the manganese compound to give a purple one.

whilst searching for uranion Sklo union glass I came across this post. Michelle I have the same bowl but in a dusky grey/dark blue, it also glows but it is a different hazy 'thick' glow compared to my other Sklo Union pieces all of which glow from a distance away from the blacklight and much brighter green although still not a 'clear 'green. I have a Schrotter lens vase (bright blue), a hobnail bowl (dark green) and also a Matura ashtray (again bright blue) which all glow REALLY brightly.

Christine, could this mean they are uranium or could they too be a result of manganese?